We are building an noise abatement enclosure (a box about 24" x 24" x 60") around a noisy piece of equipment. The enclosure is made of 3/4" MDF and is lined on the inside with 2" thick duct liner. The noise is in the audio range, from about 300Hz to a few kHz.

We are considering adding a 2nd layer of MDF to the box using green glue. However, we are concerned about the resulting weight as the enclosure must be mounted at ceiling height.

One person, who has a background in corrugated cardboard products, believes using a layer of three ply corrugated cardboard, rather than MDF, inside the enclosure would significantly attenuate the noise coming out the sides of the enclosure. He has access to the corrugated cardboard and could get it bent to fit inside the box.

Is there any merit to this? I haven't been able to find any information on the Sound Transmission Class (STC) or Noise Reduction Coefficient (NRC) of corrugated cardboard.

What does this card board weight? If the weight is considerably less then the weight of the MDF you can forget it.And even adding GG and MDF will have a marginal result; adding the MDF decoupled with a mineral wool or bonded foam filled gap is way better.

If you view life with the knowledge that there are no problems, only opportunities, you are a marketing manager.......this is my personal philosophy

I see that some people recommend use a roofing underlayment like Grace Ice and Water Shield for noise abatement. It is a 40mil (1 mm) thick butyl material with an adhesive backing. You could easily apply two layers.

How would using two layers (2 mm) of this butyl material between two layers of MDF compare to using Green Glue?

VermontDale wrote:How would using two layers (2 mm) of this butyl material between two layers of MDF compare to using Green Glue?

They are different.

I once used 30# roofing felt (A.K.A. tar paper, asphalt-saturated felt/paper, or underlayment) between two layers of plywood on a deck. It's 1.57mm (0.062 inches) thick.I did this to prevent rattles.

Green Glue is a viscoelastic compound designed for things around the mass/stiffness of drywall including plywood.

Green Glue, combined with something on both sides such as drywall/gypsum, forms a sound damping/absorbing system known as Constrained Layer Damping - i.e. when it bends it resists bending in a way that absorbs the energy.

Let's chat about constrained layer damping.

Green Glue is not glue in the traditional sense. Glue in the traditional sense creates a rigid inflexible bond between two surfaces. Green Glue is a flexible Viscoelastic membrane that converts two layers of drywall into a Constrained Layer Damping system.

This absorbs energy in the wall, not anything that's reflected, increasing TL a bit.It would reduce the coincidence dip. It would reduce the resonance dip (YEA ! YEA! YEA!)It would also reduce energy traveling down the wall (in a single layer of gypsum).

As the wall bends, the Green Glue stretches like an elastic (shear force), and converts the energy in the flexing wall to heat.

The concept of a viscoelastic material can be broken down into two parts:

A) Visco comes from the word viscosity meaning how easily a liquid pours. For example, water is not viscous and pours easily, but honey is a viscous liquid and pours very slowly. A viscous material absorbs energy when it is forced to change shape. It takes work to deform a viscous material. A lump of clay has much viscosity. It takes work to change its shape and then it holds that shape.

B) Elastic means that something can be deformed and it returns to its original shape. A rubber ball is elastic because it returns to its original shape, even after bouncing off the floor. It takes work to deform an elastic material but the material is like a spring, and stores the energy. This is why a ball bounces back.

A) + B) = C) Viscoelastic means it takes work to deform the object and also that the object returns to its original shape. But, it just doesn't spring back like a rubber ball.

Example:

If we have three balls, one of each type; visco, elastic and viscoelastic, and then we throw them one at a time on the ground, each behaves differently. The visco ball of clay hits the ground and flattens out like a pancake. The elastic ball hits the ground and bounces right back up off the ground and as round as ever. The viscoelastic ball however takes the middle road, it hits the ground and doesn't bounce up but it also doesn't flatten out, just sits there on the ground, still a completely round ball.

As far as I know cardboard does not really reduce the noise, but it does refract some of those unwanted high frequencies. I use a lair of 10 cm thick mineral cotton, a lair of 3 cm thick cardboard and some textile material as a "finish".________________________________________________Steve WorksVisit my website for more information about wall panels.